The present invention relates to a process and an apparatus for recovering metal material from waste material including organic material, such as plastic, and metal material in the form of thin foil material.
Many wastes contain valuable materials like metals, glass, paper fibers, wood and plastics. Part of the valuable materials can be rather easily separated from the waste material. E.g., paper fibers can be separated from other waste material by mixing the waste material with water. Fibers mixed with water form an aqueous suspension, which can rather easily be separated from the rest of the waste material.
It is also well known that iron may be separated from waste material by crushing the waste material and separating iron magnetically. Some metal materials may be separated from waste material by combusting the organic material in the waste and recovering metal from the combustion residue.
It is also known to combust waste, as such, in order to recover energy therefrom as thermal energy. It has further been suggested to gasify community waste or other similar waste material for providing useful product gas, which may be used for energy generation.
The combustion of waste material can, however, be difficult, if the content of metals in the waste is high and if the metals have a low melting temperature, e.g., below typical combustion temperatures, e.g., below 1100xc2x0 C. Such metals are, e.g., Al, Ag, Au, Mg, Pb, Zn and Sn. Molten metals tend to form deposits on surfaces and cause serious fouling in the waste combusting boilers. Alkali salts present in the waste material tend to increase the problem caused by deposits and fouling in combustors.
Many waste materials contain aluminum in a form which may melt already at temperatures of about 670-700xc2x0 C. Such waste material, if combusted or gasified with air, should, therefore, be treated at temperatures well below the melting point of aluminum present therein, preferably, well below 650xc2x0 C., in order to avoid problems derived from molten aluminum.
Aluminum dust may be a very hazardous component in any combustion process. Aluminum, if oxidized, may form locally very high temperatures, such as temperatures above 2000xc2x0 C., or even almost 3000xc2x0 C. Such high local temperatures in combustors can cause severe damage to the combustor. Further, aluminum in dust form is an explosive material when mixed with air. Also, metallic aluminum may react with alkali hydroxide, e.g., present in fly ash, and form aluminum hydroxide and hydrogen gas. It is well known that hydrogen gas under certain conditions may easily form explosive gas mixtures. Also, storage of fly ash with aluminum may cause problems as formation of hydrogen gas in the fly ash may continue for a long time in its dumping place.
However, many waste materials originating from the packing and insulation industry, electronic devices or components, or car demolition wastes contain such amounts of low melting metals that recovery of these is of high interest. Circuit boards, for instance, include thin foils of particularly valuable metals. E.g., etiquettes, on the other hand, contain considerable amounts of metal foils. Often, the metal is in the form of thin metal foils, the thickness usually being between 5-50 xcexcm, which renders a mechanical separation of the metal almost impossible.
The present invention sets out to provide an improved process for recovering metal material from waste material and an improved apparatus therefor, which overcomes drawbacks discussed above.
It is also an object of the present invention to provide a process and an apparatus for recovering metal material from waste material in which the heating value of plastic material present in the waste material is recovered in an optimum way.
It is a further object of the present invention to provide a process and an apparatus for recovering metal material from waste material in which metal, such as aluminum, present in the waste material, may be recovered in an optimum form.
It is a still further object of the present invention to provide a process and an apparatus for recovering metal material from waste material at a relatively low temperature, at which many problems arising from high temperatures can be avoided.
The present improved process and apparatus for recovering metal material from waste material thereby are characterized by what is more closely stated in the claims.
Thereby, a typical process for recovering metal from waste material including organic material, such as plastic, and metal material in the form of thin foil material, includes the following steps:
(a) introducing the waste material from which metal is to be recovered into a fluidized bed gasifier, for gasification of the organic material, and
(b) separating metal material from gas produced in step (a).
Correspondingly, a typical apparatus for recovering metal from waste material includes
a fluidized bed gasifier with a fluidized bed of solids therein, for gasification of the organic material in the waste material from which metal is to be recovered, and
a separator for separating metal material from gas produced in the gasifier.
Typically, metal, such as Ag, Al, Au, Mg, Pb, Zn and/or Sn, present as thin metal foils in waste material may be recovered according to the present invention. The foil material may have a thickness of about 5-50 xcexcm. In the fluidized bed, in the gasifier, the thin foil material is torn into small flakes. The actual gas velocity in the fluidized bed is to be set such that the metal flakes are entrained with the gas up to the gas outlet, but the not yet gasified waste material and bed particles stay in the bed. A slowly fluidized, bubbling fluidized bed, having a gas velocity  less than 2 m/s, typically 0.5-1 m/s, may be used. The bed typically consists of inert solid particles having a mean diameter of about 0.5 to 2 mm, typically about 1 mm.
In waste material, the metal foils are generally more or less permanently combined to some organic material, such as plastic or paper. If the waste includes polyethylene or other plastic material, which does not contain chlorine, the waste material can rather easily be gasified with air. Polyethylene has a high heating value and consists of almost 100% volatiles, which can almost totally be converted to gases and vapors in an air blown gasifier at temperatures well below the melting temperature of any aluminum present. The plastic material is thereby a very valuable fuel. A combustible gas having a high heat value of about 7-15 MJ/m3, typically 9-10 MJ/m3, may be produced in the gasifier. The gas can be used in power production or other processes utilizing combustion heat.
The temperature in the gasifier is typically maintained closed to, but just below, the melting temperature of the metal material to be recovered from the gas produced in the gasifier. The temperature thereby typically is kept below 1100xc2x0 C. Gasification of plastic material usually takes place at a temperature  less than 650xc2x0 C. Gasification of polyethylene can take place at a temperature of about 400-550xc2x0 C.
The gas produced in step (a) is typically cooled and heat energy is recovered therefrom before the metal material is separated from the gas.
If metal materials having very low melting temperatures, e.g., 200-400xc2x0 C., are to be gasified in the gasifier, then the gasification may have to be done at a higher temperature than the melting temperature of the metal. In such cases, the gas produced will include molten metal particles. The gas may be cooled in a fluidized bed gas cooler, in which the gas produced and molten particles entrained therein are mixed with cooled particles. The molten metal particles contact cooled particles and are rapidly cooled to a temperature below their melting temperature, whereafter they can be separated from the gas.
If the organic material gasified in the gasifier includes Cl, i.e., if PVC plastic material is gasified, then the produced gas can be washed after cooling to separate HCl from the gas.
The waste material from which metal is to be recovered may be pretreated by crushing and/or washing. Coarse, heavy, solid impurities may be separated from the uncrushed or crushed waste material prior to introduction of the waste material into the gasifier. Thus, e.g., iron material may be separated mechanically or magnetically from plastic material and light-weight aluminum material. Heavy solid impurities typically originate from iron scrap, refractory material or metal straps used to bind the waste material into bales.
Most heavy impurities are, as discussed above, separated from the waste material before it is introduced into the gasifier. Some heavy metal material may, however, still remain in the material introduced into the gasifier. Such remaining heavy metal impurities will be discharged from the gasifier together with bottom ash, being discharged from the bottom of the gasifier. Impurities originating from heavy metal scrap or the like is too heavy to be entrained by the upward gas flow in the gasifier and is, therefore, not mixed into the product gas and the light metal material fraction is discharged from the top of the gasifier.
Crushed or possibly uncrushed waste material may be washed or soaked in water or solvent for dissolving soluble components, such as alkali salts or other harmful components. Soluble components may thus be separated from the waste material prior to introduction of the waste material into the gasifier. Thus, e.g., alkali salts may at least partly be removed from the waste material prior to introduction thereof into the gasifier. Also, recoverable fiber material present in the waste material may be removed by washing or slushing of the waste material, prior to the introduction into the gasifier.
A conventional separator, such as a centrifugal cyclone, may be arranged downstream of the gasifier for separating the metal material being discharged from the gasifier with the gas produced in the gasifier.
The present invention provides a recycling process in which the light metal fraction of the waste material may be separated from organic material without thereby simultaneously separating and mixing into the light metal fraction other metal material or other heavy impurities possibly present in the waste material.